Process for the preparation of tetrabromobisphenol-A

ABSTRACT

Tetrabromobisphenol-A is produced in a bromination process where no bromine or only a very small proportion of bromine is fed to the reactor. In the process aqueous hydrobromic acid, is the sole source or a major source of the bromine. In the process there are at least three concurrent continuous feeds to the reactor. One is composed of bisphenol-A and/or underbrominated bisphenol-A and a water-miscible organic solvent. The second is gaseous hydrogen bromide or preferably, aqueous hydrobromic acid, and the third is aqueous hydrogen peroxide. Optionally a small additional continuous feed of bromine can be employed. The feeds are proportioned to maintain a liquid phase containing (i) from above about 15 to about 85 wt % water, based upon the amount of water and water-miscible organic solvent in such liquid phase, and (ii) an amount of unreacted bromine that is in excess over the stoichiometric amount theoretically required to convert the bisphenol-A and/or underbrominated bisphenol-A to tetrabromobisphenol-A. The tetrabromobisphenol-A continuously forms as a solids phase in a yield of at least about 90% based on bisphenol-A and/or underbrominated bisphenol-A fed. The reaction mass is agitated and/or refluxed to maintain a substantially uniform slurry in the reactor. An amount of the slurry is continuously removed so that the volume of the contents of the reactor remains substantially constant.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly-owned copending U.S.application Ser. No. 09/416,855, filed Oct. 12, 1999, the latterapplication being a continuation-in-part of commonly-owned copendingU.S. application Ser. No. 09/329,374, filed Jun. 10, 1999, which is inturn a continuation-in-part of commonly-owned copending U.S. applicationSer. Nos. 09/096,332, filed Jun. 11, 1998, now U.S. Pat. No. 6,084,136and 08/945,158, filed Oct. 21, 1997, now U.S. Pat. No. 6,084,137. U.S.application Ser. No. 09/096,332 is a continuation-in-part of U.S.application Ser. No. 08/945,158, filed Oct. 21, 1997, now U.S. Pat. No.6,084,137, which in turn is a continuation-in-part of commonly-ownedU.S. application Ser. Nos. 08/426,996 and 08/426,998 both filed Apr. 24,1995 and both now abandoned. U.S. application Ser. No. 08/426,998 inturn is a continuation-in-part of commonly-owned U.S. application Ser.No. 08/398,837, filed Mar. 6, 1995 and now abandoned. U.S. applicationNo. Ser. 08/945,158 is also a continuation-in-part of commonly-ownedU.S. application Ser. No. 08/550,044, filed Oct. 30, 1995, now U.S. Pat.No. 5,723,690, which in turn is a continuation of commonly-owned U.S.application Ser. No. 08/426,997, filed Apr. 24, 1995, now U.S. Pat. No.5,527,971.

OTHER COMMONLY-OWNED COPENDING APPLICATIONS

Reference is also made to other commonly-owned copending U.S.application Ser. Nos. 09/288,195, filed Apr. 8, 1999 and 09/407,314,filed Sep. 28, 1999.

TECHNICAL FIELD

This invention relates to novel, highly efficient processes for thepreparation of tetrabromobisphenol-A.

BACKGROUND

Tetrabromobisphenol-A is one of the most widely used brominated flameretardants in the world. It is used extensively to provide flameretardancy for styrenic thermoplastics and for some thermoset resins.

Processes used for producing tetrabromobisphenol-A generally fall intothree categories. The first category includes processes in whichsubstantial amounts of methyl bromide are co-produced along with thetetrabromobisphenol-A. Generally, up to 40-50 pounds of methyl bromidecan be expected per 100 pounds of tetrabromobisphenol-A produced. Inmost cases, the processes within this first category feature reactingbisphenol-A and bromine in methanol. The ring-bromination of thebisphenol-A is a substitution reaction which generates one mole of HBrper ring-bromination site. Thus, for the production oftetrabromobisphenol-A, four moles of HBr are generated per moleoftetrabromobisphenol-A produced. The HBr in turn reacts with themethanol solvent to produce the methyl bromide co-product. After thebisphenol-A and bromine feed are finished, the reactor contents arecooked for one to two hours to complete the reaction. At the end of thereaction, water is added to the reactor contents to precipitate out thedesired tetrabromobisphenol-A product.

The second category of processes features the production oftetrabromobisphenol-A without the co-production of substantial amountsof methyl bromide and without the use of oxidants to convert the HBr toBr₂. See for example U.S. Pat. No. 4,990,321; U.S. Pat. No. 5,008,469;U.S. Pat. No. 5,059,726; and U.S. Pat. No. 5,138,103. Generally, theseprocesses brominate the bisphenol-A at a low temperature, e.g., 0 to 20°C., in the presence of a methanol solvent and a specified amount ofwater. The water and low temperature attenuate the production of methylbromide by slowing the reaction between methanol and HBr. The amount ofwater used, however, is not so large as to cause precipitation of thetetrabromobisphenol-A from the reaction mass during the brominationreaction. Additional water for that purpose is added at the end of thereaction. This type of process typically uses a fairly long aging orcook period after the reactants have all been fed, and requiresadditional process time for the final precipitation oftetrabromobisphenol-A via the last water addition.

In the third category are those processes which feature the brominationof bisphenol-A with bromine in the presence of a solvent and,optionally, an oxidant, e.g., H₂O₂, Cl₂, etc. See for example U.S. Pat.No. 3,929,907; U.S. Pat. No. 4,180,684; U.S. Pat. No. 5,068,463 andJapanese 77/034620 B4 77/09/05. The solvent is generally awater-immiscible halogenated organic compound. Water is used in thereaction mass to provide a two-phase system. As the bisphenol-A isbrominated, the tetrabromobisphenol-A is formed in the solvent. Theco-produced HBr is present in the water. When used, the oxidant oxidizesthe HBr to Br₂, which in turn is then available to brominate morebisphenol-A and its under-brominated species. By oxidizing the HBr toBr₂, only about two moles of Br₂ feed are needed per mole of bisphenol-Afed to the reactor. To recover the tetrabromobisphenol-A from thesolvent, the solution is cooled until tetrabromobisphenol-Aprecipitation occurs. The cooling of the solution to recovertetrabromobisphenol-A entails additional expense and process time.

Process technology for producing tetrabromobisphenol-A is described incommonly-owned U.S. Pat. Nos. 5,527,971, 5,723,690, 5,847,232,6,002,050, 6,084,136, and 6,084,137, and in commonly-owned U.S. patentapplication Ser. Nos. 09/288,195, filed Apr. 8, 1999, 09/329,374, filedJun. 10, 1999, 09/407,314, filed Sep. 28,1999, and 09/416,855, filedOct. 12, 1999.

THE INVENTION

This invention makes it possible to produce tetrabromobisphenol-A on acontinuous basis wherein the use of bromine feeds can be eliminated orat least greatly minimized, wherein steady state operation can berapidly achieved after plant startup, and wherein such steady stateoperation can be maintained with minimal process controls. At the sametime these objectives can be achieved without sacrifice of otheradvantageous features of the commonly-owned technology, such as formingduring the bromination precipitated tetrabromobisphenol-A that is highlypure, of minimal, if any, color, readily recoverable, and formed in highyield based on the bisphenol-A fed to the reaction.

The processes of this invention thus feature the efficient production ofhigh-quality, low-color tetrabromobisphenol-A in high yields underoperating conditions that avoid localized concentrations of bromine inthe reaction mass and that make possible the maintenance of abromination reaction mass of substantially uniform compositionthroughout substantially the entire bromination reaction. Although theprocesses of this invention can be run in a semi-continuous mode, thegreatest benefits are achievable when the operation is conducted in acontinuous mode. When run in a semi-continuous mode, process efficiencyis enhanced due to relatively short reaction times and the absence of aneed for a time-consuming one hour plus post-reaction cook period or apost-reaction tetrabromobisphenol-A precipitation step. The use of acontinuous process for the production of tetrabromobisphenol-A is ararity in itself and is made possible by the short reaction andtetrabromobisphenol-A precipitation times which are features ofprocesses of this invention. In the continuous mode, reactor size can besubstantially reduced without a loss in product output.

In addition to the above reaction efficiencies, the processes of thisinvention are capable of producing high yields of tetrabromobisphenol-Ain a methanol- or ethanol-based solvent without the substantialconcomitant production of methyl bromide or ethyl bromide, e.g., aslittle as 0.2 to 1.0 lbs (ca. 0.09 to ca. 0.45 kg) of methyl bromide orethyl bromide per 100 lbs (ca. 45.4 kg) of tetrabromobisphenol-Aproduct. Even further, it is possible to obtain high yields of almostpure white tetrabromobisphenol-A even though excess unreacted bromine ispresent in the reaction mass during substantially all of the time steadystate bromination conditions have been established.

Pursuant to this invention there is provided in one of its embodiments aprocess of producing tetrabromobisphenol-A, which process comprises:

a) concurrently feeding to a reactor (i) a first continuous feed streamcomposed of bisphenol-A and/or underbrominated bisphenol-A and awater-miscible organic solvent, (ii) a second continuous feed composedof gaseous hydrogen bromide and/or aqueous hydrobromic acid, and (iii) athird continuous feed composed of aqueous hydrogen peroxide, at relativerates that maintain in the reactor during at least a substantial portionof such concurrent feeding, a reaction mass having a liquid phasecontaining from above about 15 to about 85 wt % water, and preferably inthe range of about 30 to about 85 wt % water, the wt % being based uponthe amount of water and water-miscible organic solvent in the liquidphase of the reaction mass;

b) during at least a substantial portion of the concurrent feeding ina), maintaining the temperature of the reaction mass within the range ofabout 30 to about 100° C.;

c) during at least a substantial portion of the concurrent feeding ina), providing the continuous feeds at relative rates (i) that maintainin the liquid phase of the reaction mass an amount of unreacted brominethat is in excess over the stoichiometric amount theoretically requiredto convert the bisphenol-A and/or underbrominated bisphenol-A totetrabromobisphenol-A, and to continuously form during substantially allof the time the feeding in a) is occuring, a precipitate comprisedmainly of tetrabromobisphenol-A, and (ii) that result in a yield ofprecipitated tetrabromobisphenol-A during substantially all of the timethe feeding in a) is occurring of at least about 90% based on the amountof the bisphenol-A or underbrominated bisphenol-A or combination thereoffed up to that point in time; and

d) during at least a substantial portion of the concurrent feeding ina), withdrawing from the reactor a mixture of precipitatedtetrabromobisphenol-A and a potion of the liquid phase of the reactionmass, such that the volume of the contents of the reactor remainssubstantially constant during at least a substantial portion of theconcurrent feeding in a).

Reference anywhere in this document to bromine in the liquid phase ofthe reaction mass should be understood to mean unreacted bromine, asdistinguished from total bromine which would include both unreacted andreacted bromine. And as any chemist would readily understand, referenceto unreacted bromine in the liquid phase does not include the brominecontent of HBr present in the liquid phase.

When conducting the processes of this invention it is preferred that noelemental bromine be fed into the reactor. In other words, except for apossible charge of elemental bromine as part of a heel to initiate thecontinuous process, it is preferred to rely entirely on the hydrogenbromide and/or the hydrobromic acid fed to the reactor plus the HBrco-product of the bromination that remains in the liquid phase of thereaction mass as the source of the bromine for the bromination, thebromine thus being totally formed in situ. However, it is possiblepursuant to this invention to continuously feed elemental bromine in anamount constituting a small portion of the total bromine requirementsfor the process. In such case the process is conducted using theconcurrent feeds described above while also concurrently feedingelemental bromine into the reactor (most preferably widely distributedat locations below the surface of the liquid phase of the reactionmass), the bromine feed being at a substantially constant rate and inquantity such that the mole ratio of Br₂ to HBr being fed does notexceed about 0.5:1.

In another embodiment of this invention there is provided a process forthe production of tetrabromobisphenol-A, which process comprises:

a) providing a steady-state liquid phase reaction system to which atleast a first feed of bisphenol-A and/or underbrominated bisphenol-A anda water-miscible organic solvent, a second feed of gaseous hydrogenbromide and/or aqueous hydrobromic acid, and a third feed of aqueoushydrogen peroxide, are being continuously fed and in which there isbeing continuously formed a tetrabromobisphenol-A precipitate by thebromination of bisphenol-A and/or underbrominated bisphenol-A with anexcess of bromine over the stoichiometric amount theoretically requiredto produce tetrabromobisphenol-A, and in which

1) all of the bromine in the steady-state liquid phase reaction system(i.e., excluding the startup of the process where bromine may be used ifdesired) is formed in situ by reaction between the HBr and the H₂O₂, or

2) a portion, but no more than 50 mole percent, and preferably no morethan 10 mole percent, of the bromine is continuously fed into the systemas bromine, with the balance of the bromine being formed in situ byreaction between the HBr and the H₂O₂,

such that tetrabromobisphenol-A is being formed continuously in a yieldof at least about 90% based on the amount of the bisphenol-A and/orunderbrominated bisphenol-A already fed;

b) agitating and/or refluxing the reaction system so as maintain asubstantially uniform slurry within the reaction system; and

c) continuously separating from the reaction mass, an amount of thesubstantially uniform slurry to continuously maintain the reactionsystem at substantially constant volume.

In both of the above embodiments it is preferred to employ aqueoushydrobromic acid rather than gaseous hydrogen bromide as the externalsource of bromine for the process. Among the reasons for this is thatthe aqueous hydrobromic acid contributes to maintenance of the watercontent of the reaction mass which is a necessary feature of theprocess. Also, close control of liquid feeds such as aqueous hydrobromicacid is generally more readily achieved than with gaseous feeds such ashydrogen bromide. Moreover, the feed of aqueous hydrobromic acid to awater-containing reaction mass is less likely to result in localizedexcess concentrations of HBr within the reaction mass.

A further embodiment of this invention is a bromination process in whichtetrabromobisphenol-A is produced with little or no bromine being fed tothe bromination reaction mass, the process being characterized bymaintaining at least three concurrent separate continuous feeds to areaction mass having a liquid phase composed of a water-miscible organicsolvent and water, these three feeds being composed of (1) bisphenol-Aand/or underbrominated bisphenol-A and the water-miscible organicsolvent, (2) aqueous hydrobromic acid, and (3) aqueous hydrogenperoxide. These feeds are being proportioned and the reaction mass isbeing maintained at a temperature such that under steady-state reactionconditions:

a) bromine and water are being continuously formed in situ by oxidationof HBr by H₂O₂,

b) tetrabromobisphenol-A is being continuously formed via bromination asa solids phase in an overall yield of at least about 90% based on theamount of the bisphenol-A and/or underbrominated bisphenol-A alreadyfed,

c) hydrogen bromide is being continuously formed in situ as a co-productof the bromination in b),

d) an excess amount of unreacted bromine is continuously present in theliquid phase of the reaction mass, and

e) the amounts of water being fed and being generated in situcontinuously maintain the water content in the liquid phase of thereaction mass high enough to cause the tetrabromobisphenol-A tocontinuously precipitate from the liquid phase substantially at the sametime tetrabromobisphenol-A is being continuously formed.

An optional feature of this embodiment involves providing a portion, butno more than 50 mole percent, and preferably no more than 10 molepercent, of the bromine in the liquid phase of the reaction mass bycontinuously feeding this portion of bromine into the reaction mass asbromine, with the balance of the bromine being formed in situ byreaction between the HBr and H₂O₂ being fed. Another feature of thisembodiment is to mechanically agitate and/or reflux the reaction mass tomaintain substantial uniformity in the reaction mass. Continuouslyseparating a portion of the substantially uniform reaction mass from theremainder of the reaction mass, preferably in an amount to continuouslymaintain the reaction mass at substantially constant volume, areadditional features of this embodiment.

Important features of this invention are that not only is thebromination reaction very rapid especially under preferred temperatureconditions used (from about 50 to about 100° C.), but during all orsubstantially all of the time the reactants (Br₂ and bisphenol-A and/orunderbrominated bisphenol-A) are coming in contact with each other inthe liquid phase of the reaction mass under the specified conditions, aprecipitate is being formed that (i) typically contains at least about90 wt %, and preferably at least about 95 wt % of tetrabromobisphenol-A,and (ii) typically is formed in a yield of at least about 90% based onthe amount of bisphenol-A and/or underbrominated bisphenol-A fed to thereaction mass. Moreover, even though the liquid phase of the reactionmass contains at substantially all times during the concurrent feeds anamount of unreacted bromine—perhaps as much as 20,000 ppm of unreactedbromine, but preferably no more than about 10,000 ppm—thetetrabromobisphenol-A being produced is of low color (e.g. it will havean APHA color of 100 or less, and usually 50 or less, the APHA colorbeing determinable by dissolving 80 grams of the tetrabromobisphenol-Aproduct in 100 mL of acetone).

Rapid, high yield formation of the tetrabromobisphenol-A product as aprecipitate facilitates the recovery of the product, as this can beeffected by any of a variety of physical separation procedures such asdraining, decantation, centrifugation, and/or filtration. Moreparticularly, the precipitate enriched in the desired product is removedfrom the reaction mass continuously or substantially continuously, alongwith a portion of the reaction mass, whereby the volumes of feeds to,and material removed from, the reactor are kept constant orsubstantially constant at all times. The presence in the liquid phase ofthe reaction mass of excess unreacted bromine over and above thatrequired to convert the bisphenol-A and/or underbrominated bisphenol-Ato tetrabromobisphenol-A ensures that this desired product is formed inhigh yield without significant contamination by underbrominatedbisphenol-A such as tribromobisphenol-A. And since all, or substantiallyall of the bromine is produced in situ by rapid oxidation of HBr byhydrogen peroxide with both such reactants in the liquid phase, it ispossible to engender bromine formation substantially uniformlythroughout substantially the entire liquid phase of the reaction mass,e.g., by use of agitation or by refluxing the liquid phase, or both.This in turn eliminates localized concentrations of bromine, such as canoccur when rapidly feeding large amounts of elemental bromine to thereaction mass. Use of such agitation or refluxing also ensures that theliquid feed of bisphenol-A and/or underbrominated bisphenol-A plusorganic solvent entering the liquid phase of the reaction mass is alsosubstantially uniformly distributed throughout the reaction mass.Consequently, the tetrabromobisphenol-A particles are formedsubstantially uniformly throughout the reaction mass, and therefore thetetrabromobisphenol-A precipitate plus the portion of the reaction massbeing continuously removed from the reactor remains substantiallyuniform in composition during substantially the entire time theconcurrent feeds are taking place. Thus once steady state conditionshave been achieved, continuous operation of the process requires aminimum of process controls.

The HBr fed to and generated in situ as the by-product of thebromination reaction serves at least a dual role in the process. First,the HBr in the water-containing reaction mass tends to keep thetetrabromobisphenol-A from developing color as it thetetrabromobisphenol-A is being formed as a precipitate in the reactionmass. Secondly, the HBr serves as the sole source, or at least a majorsource, of the bromine used in the bromination reaction. In addition,the use of aqueous hydrobromic acid as one of the concurrent feedsavoids the difficulties that can arise when feeding a gaseous reactant(e.g., incorrect or imprecise metering into the reaction mass).Moreover, use of an aqueous hydrobromic acid feed serves as a way offeeding a significant portion of the water to maintain the desiredcomposition of the liquid phase of the reaction mass during theconcurrent feeds by contributing to the replenishment of the waterconcurrently being withdrawn from reactor as part of the reaction massthat is being withdrawn from the reactor along withtetrabromobisphenol-A precipitate.

The fact that a substantial quantity of water is continuously maintainedin the liquid phase of the reaction mass contributes to the highefficiency of the process. In the first place, the water in the liquidphase causes the tetrabromobisphenol-A product to precipitate from theliquid phase essentially as soon as the tetrabromobisphenol-A is formed.Such continuous rapid precipitation occurs because the quantity of waterpresent in the liquid phase provides a liquid medium in which thetetrabromobisphenol-A is quite insoluble. Secondly, the water in theliquid phase of the reaction mass contributes significantly to theretention in the liquid phase of a large proportion of the HBr as it isbeing co-produced from the continuous bromination. That is to say,hydrobromic acid is formed in situ by interaction of HBr co-product andwater in the reaction mass. Thus losses of HBr to the headspace in thereactor, if any, arc typically very small. This in turn ensures thatmost, if not all, of the HBr retained in the liquid phase will beconverted in situ to bromine via oxidation by the hydrogen peroxidebeing charged to the reactor. Thus there is at least a duality offunction for the water in the liquid phase of the reaction mass. Asnoted hereinafter, it is believed that still another function served bythe water is that of controlling of the amount of alkyl bromideco-product formed when the water-miscible solvent used is an alcohol.

Since excess bromine is to be present in the liquid phase in thereactor, the source of the bromine thus consists of (i) brominegenerated in situ by oxidation of HBr or (ii) a combination of arelatively small proportion of bromine fed to the reactor in liquidand/or gaseous form plus a relatively large proportion of brominegenerated in situ by oxidation of HBr. The HBr that is oxidized tobromine is typically a combination of HBr co-product from thebromination plus HBr fed to the reactor. While in theory it may bepossible to use only HBr fed to the reactor as the source of HBrsubjected to the in situ oxidation, this would require segregating thecoproduct HBr from the HBr fed to the reactor.

In the practice of this invention the amount of unreacted brominemaintained in the liquid phase of the reaction mass typically will notexceed about 3.5 wt % (ca. 35,000 ppm). Preferably the amount of brominein the liquid phase of the reaction mass is kept in the range of about50 to about 20,000, and more preferably in the range of about 50 toabout 10,000 parts per million (ppm) during substantially the entirebromination period. As can be seen from the foregoing, and as isconventional, all parts referred to in any portion of this document areby weight unless otherwise expressly indicated.

In conducting the concurrent feeds referred to above, once steady-statereaction conditions have been established, it is most preferred tomaintain all feeds on a uniform continuous basis to thereby maintain asteady-state liquid phase reaction system. However, minor fluctuationsin the concentrations of the respective feeds or temporary shortinterruptions in one or more of the feeds can be tolerated as long assuch fluctuations or interruptions do not cause an irreparable loss ofthe steady-state reaction conditions.

This invention in its various forms referred to above thus provides inessence a process wherein tetrabromobisphenol-A product is produced byproviding a liquid phase reaction system in which there is directlyformed a tetrabromobisphenol-A precipitate by the bromination ofbisphenol-A and/or underbrominated bisphenol-A. The bromination involvesuse of an excess of bromine over the stoichiometric amount theoreticallyrequired to produce tetrabromobisphenol-A. All, or at least the vastmajority of the bromine in the reaction system is generated in situ fromHBr, at least part of which is continuously fed as HBr, preferably asaqueous hydrobromic acid. Typically HBr co-product is also oxidized insitu to bromine. The bromination is thus conducted in the presence of anamount of HBr that is high enough to protect the tetrabromobisphenol-Abeing produced from excessive color development. Moreover, thebromination is conducted at such rate that (i) there is insufficientopportunity for significant precipitation of the intermediate,tribromobisphenol-A, to occur, and (ii) while the bisphenol-A and/orunderbrominated bisphenol-A is/are being brought into contact withunreacted bromine in the liquid phase of the reaction mass,tetrabromobisphenol-A is being produced substantially continuously.Typically the yield of the tetrabromobisphenol-A as it is being producedsubstantially continuously is at least about 90%, and preferably atleast about 95% based on the amount of the bisphenol-A and/orunderbrominated bisphenol-A already fed. In addition thetetrabromobisphenol-A produced typically has an APHA color of less thanabout 100, preferably 50 or less, the APHA color being determinable bydissolving 80 grams of the tetrabromobisphenol-A product in 100 mL ofacetone.

Other embodiments and features of the invention will become stillfurther apparent from the ensuing description and appended claims. Theensuing description refers primarily to the conduct of the processes ofthis invention once steady-state operating conditions have beenachieved. Conditions for process initiation or startup which may differto some extent from steady-state conditions are identified in the text.

As noted above, the organic reactant used in the practice of thisinvention is bisphenol-A and/or underbrominated bisphenol-A. The term“underbrominated bisphenol-A” refers to one or more brominatedbisphenol-A compounds in which less than the four ortho-positionsrelative to the hydroxyl groups are substituted by a bromine atom.Typically, the major underbrominated bisphenol-A species is thetribrominated species(3,5-dibromo-4-hydroxyphenyl)(3-bromo-4-hydroxyphenyl)dimethylmethane),but one or more other underbrominated species may be present such aseither or both of the dibromo species,3,5-dibromo-4-hydroxyphenyl)(4-hydroxyphenyl)dimethylmethane andbis(3-bromo-4-hydroxy-phenyl)dimethylmethane, and/or the monobromospecies (3-bromo-4-hydroxyphenyl)(4-hydroxyphenyl)dimethylmethane.Therefore the organic reactant fed to the reactor can be bisphenol-Aonly, any one of these underbrominated bisphenols only, any combinationof any two or more of these underbrominated bisphenol-A species only, orany combination of bisphenol-A and any one or more of theseunderbrominated bisphenol-A species. The preferred organic reactant fedto the reactor is bisphenol-A itself. Of course during the bromination,the bisphenol-A is transformed into various underbrominated bisphenol-Aspecies until it becomes tetrabromobisphenol-A. The same holds true forthe various underbrominated bisphenol-A species which during brominationfinally become tetrabromobisphenol-A. Therefore the term “bisphenol-Aand/or underbrominated bisphenol-A” in this document refers to theidentity of the compound as it exists prior to being fed into thebromination reaction mass.

The water-miscible organic solvent can be defined functionally as amaterial which is capable of solvating Br₂, bisphenol-A,monobromobisphenol-A, dibromobisphenol-A and tribromobisphenol-A underreaction conditions. Further, the organic solvent should besubstantially inert with regard to Br₂, H₃OBr and the ring-brominationof the bisphenol-A to tetrabromobisphenol-A and not contribute to theproduction of troublesome amounts of color bodies, ionic bromides and/orhydrolyzable bromides. Hydrolyzable bromides can include 1-bromo-2-alkoxy-2-(3′,5′-dibromo-4′-hydroxyphenyl)propane,1,1-dibromo-2-alkoxy-2-(3′,5′-dibromo-4′-hydroxyphenyl)propane,1,3-dibromo-2-alkoxy-2-(3′,5′-dibromo-4′-hydroxy-phenyl)propane, and1,1,3-tribromo-2-alkoxy-2-(3′,5′-dibromo-4′-hydroxyphenyl)propane. Thesolvent, when taken in combination with the water and reactionconditions of the processes of this invention, can have some smallability to solvate tetrabromobisphenol-A, but for the sake of reactionyield, the solvating power should be low, say no more than about 20 wt %and preferably no more than about 5 wt % solvated tetrabromobisphenol-Ain the liquid phase of the reaction mass.

Exemplary of the preferred water-miscible organic solvents arewater-miscible alcohols (eg., methyl alcohol, ethyl alcohol, n-propylalcohol, isopropyl alcohol, tert-butyl alcohol), water-misciblecarboxylic acids, (e.g., acetic acid, propionic acid), andwater-miscible nitriles, (e.g., acetonitrile). Some water-miscibleethers may also be suitable provided they are not cleaved by the acidicnature of the reaction mass. Mixtures of two or more suitable organicsolvents can be employed. The more preferred solvents are the alcoholshaving up to 4 carbon atoms. Even more preferred are ethanol andmethanol as they are relatively inexpensive and are easily recovered bysimple distillation techniques for recycle. Ethanol is most preferred.It is to be understood and appreciated that the organic solvent need notbe soluble in water in all proportions at, say, 20° C. Although suchtotal miscibility is preferable, the organic solvent should at leasthave sufficient solubility in water in the proportions and at thebromination temperature(s) being employed to form a clear one-phasehomogeneous liquid reaction medium from which tetrabromobisphenol-Aproduct will precipitate during the bromination.

The amount of water-miscible organic solvent used is best related to theamount of bisphenol-A fed and can be conveniently expressed as theweight ratio of the organic solvent to bisphenol-A. Typically, the ratiois within the range of from about 1:1 to about 10:1, preferably withinthe range of from about 2:1 to about 10:1, and most preferably the ratiois within the range of from about 3:1 to about 5:1. More or less organicsolvent can be used, provided that the solvent function mentioned aboveis accomplished.

The water-miscible organic solvent is preferably fed to the reactor as aconstituent of a solution or slurry of bisphenol-A and/orunderbrominated bisphenol-A. However, if desired, only a portion of theorganic solvent can be fed as part of the bisphenol-A and/orunderbrominated bisphenol-A solution or slurry, with the remainingportion, generally a smaller portion, being fed as a separate stream.The temperature of the feed stream of the solution or slurry ofbisphenol-A and/or underbrominated bisphenol-A in the water-miscibleorganic solvent should be such as to result in efficient operation, andthe temperature selected for the feed should take into consideration thedesired reaction mass temperature to be used. Thus the feed stream canbe fed at room temperature, or at a temperature above or below roomtemperature, and therefore, the temperature selected for the feed streamcan be used as a way of assisting in the regulation of the reaction masstemperature. However, the temperature of the feed stream should not beabove the boiling temperature or below the freezing temperature of thewater-miscible organic solvent, or otherwise result in interfering withthe continuous free flow of the feed stream into the reactor. Also, thetemperature of this feed stream should not detrimentally cool or heatthe reaction mass. The foregoing comments with regard to temperaturealso apply to that portion of the water-miscible organic solvent thatmay be separately fed into the reactor, if any such separate feed is tobe employed.

When the water-miscible organic solvent used is ethanol, it is preferredto produce no more than about 4.54 kg (10 lbs) of ethyl bromide per 45.4kg (100 lbs) of tetrabromobisphenol-A precipitate produced.

HBr, preferably as aqueous hydrobromic acid, constitutes another of theconcurrent continuous feeds to the reactor. Aqueous hydrobromic acidbeing fed will typically be a solution containing in the range of about10 to about 50 wt % of HBr, and preferably will contain in the range ofabout 20 to about 50 wt % of HBr. Most preferably the HBr content is inthe range of about 40 to about 48 wt % of HBr. This feed stream can beintroduced while at room temperature, or it can be fed at a suitabletemperature above or below room temperature to assist in maintaining thedesired temperature reaction mass during steady-state operatingconditions.

Another concurrent feed to the reactor is aqueous hydrogen peroxide.Although it is possible pursuant to this invention to use other oxidantmaterials, e.g., small proportions of chlorine, to generate bromine insitu, aqueous hydrogen peroxide is by far the most preferred oxidant.The function of the oxidant is to oxidize HBr to Br₂ in the reactionmass and under the process conditions of this invention, and it must doso without materially interfering with the bromination reaction. Safetyconsiderations make it desirable to feed the H₂O₂ to the reaction massas an aqueous solution containing no more than about 90 wt % H₂O₂.Preferred are aqueous solutions containing from about 20 to about 80 wt% H₂O₂. A more preferred solution is one containing from about 30 toabout 70 wt % H₂O₂, with a solution containing about 30 to about 50 wt %H₂O₂, being especially preferred. The use of a continuous aqueous feedto the reactor of hydrogen peroxide is also advantageous in that thefeed assists in maintaining the appropriate water level in the reactionmass by compensating in part for the water that is being removed as partof the reaction mass concurrently being removed from the reactor.Usually this feed stream will be fed while it is at about roomtemperature, although some departure from room temperature can beresorted to as long as the temperature does not cause decomposition ofthe solution or otherwise adversely interfere with the brominationreaction conditions in the reaction mass.

If bromine is to be fed during reaction startup or as one of theconcurrent feeds to the reactor when operating under steady statereaction conditions, use can be made of commercially available Br₂ ofsuitable purity. Should the Br₂ contain undesirable impurities, it canbe treated by conventional purification techniques, e.g., distillation,H₂SO₄ treatment, etc., which are well known to those skilled in the art.

The Br₂, if and when fed to the reactor, can be fed as a liquid or as agas. It is preferred that the feed be gaseous. Whether the Br₂ is liquidor gaseous, it is preferred that the feed entry point be sub-surface ofthe reaction mass. This is conveniently accomplished by use of one ormore dip tubes. Preferably the ports of entry for the bromine are widelydisseminated in the reaction mass so that the feed is spread out in arelatively uniform manner in the reaction mass, and so that theindividual ports discharge small portions of the total feed therebyminimizing the possibility of localized high concentrations of bromine.If the feed is liquid, above-surface feed must contend with possiblesplattering, bromine loss due to evaporation, and inefficient mixing.

When bromine is fed to the reactor, the Br₂ is preferably at atemperature which promotes process efficiency in view of the desiredreaction mass temperature. A suitable liquid Br₂ feed temperature isfrom about 10° C. to just below the boiling point of Br₂. If the Br₂ isto be fed as a gas, then the Br₂ stream temperature should be that whichis conducive to such a feed. For example, such a feed temperature may bewithin the range of from about 60 to about 100° C. The solution feedtemperature should be that which does not detrimentally cool or heat thereaction mass or which requires pressure operation so that the feed canbe made in the liquid state.

The amount of water in the reaction mass should be within the range offrom above about 15 to about 85 wt %, and typically is in the range ofabout 30 to about 85 wt % of water, based upon the total amount of waterand water-miscible organic solvent in the liquid phase of the reactionmass. Preferably, the amount of water fed is that amount which is withinthe range of from about 30 to about 75 wt % water. Most highly preferredis the range of from about 30 to about 70 wt %. When the water-miscibleorganic solvent is methanol the preferred amount is from about 30 toabout 55 wt %. With ethanol, the preferred amount of water is from about40 wt % to about 65 wt %.

The water content of the reaction mass is an important aspect of thisinvention. Although this invention is not to be limited in any way byany particular theory, it is believed that the water content suppressesformation of methyl bromide or ethyl bromide and, at the same time,allows for production of high purity tetrabromobisphenol-A product.Normally, it might be expected that the water content would causeunder-brominated species, e.g., tribromobisphenol-A, to precipitatealong with the tetrabromobisphenol-A species, thereby yielding an impureproduct. However, the processes of this invention are in fact capable ofproducing product of desirable purity as well as product with little, ifany, color.

It is possible to feed a portion of the water to the reactor as part ofa solution or slurry which also contains bisphenol-A and/orunderbrominated bisphenol-A and a water-miscible solvent. It is alsopossible to introduce part of the water into the reaction mass as aseparate feed stream. This latter feed, if used, should be concurrentwith the other feeds referred to above. Preferably, however, all of thewater being introduced into the reactor, is fed by means of a feed ofaqueous hydrobromic acid, and the concurrent feed of aqueous hydrogenperoxide solution, as this minimizes process controls. It should be keptin mind that two moles of water are formed in the reactor from each twomoles of HBr that are oxidized to a mole of diatomic bromine by a moleof H₂O₂. No matter how the water is provided to the reaction mass, thechief requirement is that the proper amount of water be maintained inthe reaction mass during substantially all of the reaction period sothat precipitation of tetrabromobisphenol-A occurs as the bromination isproceeding.

The concurrent feeds to the reactor all contribute to the formation ofthe reaction mass in the reactor. These feeds will produce a reactionmass liquid phase (liquid portion) and, because of the formation oftetrabromobisphenol-A precipitate, ultimately, but rather quickly, areaction mass solid phase (solid portion). Typically, the reaction massis agitated and/or maintained under continuous reflux, such that thereaction mass is in the form of a substantially uniform slurry, withsome small amount of non-uniformity due principally to the effect ofgravity upon the reaction mass. A portion of the Br₂ in the reactionmass resulting from in situ oxidation of HBr and, if used, a limitedfeed of bromine, be it fed as a gas or as a liquid, will be consumed inthe bromination reaction. Any non-consumed Br₂ feed will be found in theliquid phase and will be joined there by any non-consumed Br₂ producedby the oxidation of HBr present in the reaction mass.

The liquid phase of the reaction mass should continuously contain anexcess of unreacted bromine relative to the amount of bisphenol-A and/orunderbrominated bisphenol-A being continuously maintained in the liquidphase of the reaction mass. A stoichiometric amount of bromine is onemolecule of diatomic bromine (Br₂) for each hydrogen atom present as asubstituent in an ortho-position relative to the hydroxyl groups ofbisphenol-A and/or underbrominated bisphenol-A present in the reactionmass. For example, if the feed were 1 mole of bisphenol-A and 1 mole oftribromobisphenol-A, there would be a total of 5 moles of hydrogen atomsin the ortho positions—i.e., 4 moles in the bisphenol-A and 1 mole inthe tribromobisphenol-A. A stoichiometric amount of bromine in thisparticular case would therefore be equivalent to 5 moles of diatomicbromine, and pursuant to this invention an amount of bromine equivalentto more than 5 moles of bromine would be continuously maintained in theliquid phase of the reaction mass. Similarly, if the feed were, say, 1mole of mono-orthobromobisphenol-A, there would be a total of 3 moles ofhydrogen atoms in the ortho positions. A stoichiometric amount ofbromine in this particular case would therefore be equivalent to 3 molesof diatomic bromine, and pursuant to this invention an amount of bromineequivalent to more than 3 moles of bromine would be continuouslymaintained in the liquid phase of the reaction mass. In accordance withthis invention either (a) all of the bromine required for thebromination and to maintain the excess amount of unreacted bromine inthe liquid phase of the reaction mass is generated in situ by oxidationof HBr, or (b) up to 50 mole %, and preferably up to 10 mole % of suchbromine requirements is being fed as bromine itself with the balancebeing generated in situ by oxidation of HBr. Whichever such method usedin providing these bromine requirements, the amount of unreacted brominespecified above should be continuously maintained in the liquid phase ofthe reaction mass.

As just pointed out, unreacted bromine in the liquid phase of thereaction mass should be present at all times during the concurrent feedsto the reactor. However, it is permissible, although not desirable, tomake or to endure brief departures from this highly advantageousoperating condition. In other words it is possible for the unreacted Br₂content in the reaction mass to disappear for brief periods of timedepending on the level of underbrominated species that can be toleratedin the tetrabromobisphenol-A reaction product and/or upon the extent ofprecipitation of the underbrominated species which is experienced. Forbest results, steady-state operating conditions should be reinstated asquickly as possible after such disappearance of bromine content from thereaction mass, so that more efficient operation is resumed andmaintained. It is desirable when establishing the process parameters tobe used in a given situation to observe the process and determine byempirical methods the sensitivity of the chosen reaction conditions tothe brief absence of unreacted Br₂ in the reaction mass. Thus, for thepurposes of this invention the feature of maintaining in the liquidphase of the reaction mass an amount of unreacted bromine that is inexcess over the stoichiometric amount theoretically required to convertthe bisphenol-A and/or underbrominated bisphenol-A totetrabromobisphenol-A encompasses brief periods of time in which theunreacted bromine content can be nil, but which does not result in theformation of underbrominated species to an extent that results in anunacceptable tetrabromobisphenol-A product, say, one containing lessthat about 96 wt % tetrabromobisphenol-A.

In producing bromine from HBr, the stoichiometry involves two moles ofHBr and one mole of hydrogen peroxide to form one mole of diatomicbromine (Br₂). Two moles of water are co-produced. Among the advantagesof this invention is that both the bromination and the in situ HBroxidation reactions are rapid, especially when operating with thereaction mass temperature within the range of about 30 to about 100° C.,and especially in the range of about 60 to about 100° C.

Another advantage of the processes of this invention is that HBr is arelatively inexpensive bromine source. Gaseous HBr is often produced insubstantial quantities in various industrial chemical processes, and itis relatively easy to convert such HBr to hydrobromic acid by dissolvingthe HBr in water. Moreover, it is not necessary to closely control theamount of aqueous hydrobromic acid being fed to the reactor as long asthe desired water content of the liquid phase of the reaction mass isnot exceeded. The amount of bromine being generated in situ from the HBrpresent in the liquid phase (fed HBr and co-product HBr) of the reactionmass can be regulated and controlled by regulating the amount ofhydrogen peroxide being fed to the reaction mass. The excess unreactedHBr can thus be recovered from the liquid phase of the reaction massbeing continuously withdrawn from the reactor and used as recycle to theprocess.

While on the subject of stoichiometry, it will be recalled that forevery atom of bromine introduced into the bisphenol-A or underbrominatedbisphenol-A molecule during the bromination, one molecule of HBr isproduced. In other words, for every mole of diatomic bromine (Br₂) thatreacts with the bisphenol-A or underbrominated bisphenol-A, one mole ofHBr coproduct is produced. Therefore this HBr that is automaticallygenerated in situ should be taken into consideration in designing thefeeds and feed rates to be used in the reaction in order to maintain therequisite amount of HBr in the liquid phase of the reaction mixture.Although most of such coproduct HBr will usually remain in the liquidphase, some HBr may escape into the headspace of the reactor. The amountof such vaporized HBr will depend on such factors as the rate at whichthe bromination reaction is proceeding, the amount of water present inthe liquid phase, the rate of agitation, if any, being used, and thepressure conditions in the reactor. Therefore, in any given situationwhere the conditions for producing and maintaining the particular amountof HBr desired in the liquid phase of the reaction mass during the timethe reactants are being brought into contact with each other so thatbromination is taking place, are not already known, it is desirable toperform a few preliminary pilot experiments in which the calculatedfeeds are adjusted to achieve the optimal conditions for achieving thedesired amount of HBr in the liquid phase of the reaction mass.

Thus, quantifying for a selected set of operating conditions thepreferred target amount of unreacted Br₂ to be present in the reactionmass liquid phase is best handled by a trial and error technique. Atrial process is first defined by choosing an unreacted Br₂ target leveland the other process parameters. The produced tetrabromobisphenol-Aproduct from the process is analyzed for its tri- andtetrabromobisphenol-A content. If the tribromobisphenol-A level is toohigh, another trial process is constructed with a higher targetunreacted Br₂ level. The procedure is repeated until the desired productis obtained. It is to be noted that some benefit towards reducing thetribromobisphenol-A content in the precipitate can also be obtained byusing a higher reaction temperature. As the chosen unreacted Br₂ contentgets higher, care should be taken that the unreacted Br₂ content willnot be so high that it results in the production of tribromophenol andother by-products which are not desirable from a commercial standpoint.

Quantitative determination of the amounts of unreacted bromine and HBrin the liquid phase of the reaction mass is best conducted by samplingthe reaction mass at intervals during the bromination, removing solidsfrom the samples and analyzing the samples for their contents of bromineand HBr. While the particular methods of analysis used are not criticalas long as they are of suitable accuracy and precision, the followingoverall analytical procedures are recommended:

Determination of Unreacted Bromine:

A weighed aliquot of the clear reaction mass mother liquor (about 1 mLsample) is dispersed into 100 mL of 2% potassium iodide solution. Starchis added as an indictor. Blue color indicates the presence of bromine.The stirred mixture is titrated against 0.01 N sodium thiosulfatesolution to a clear end point. Unreacted bromine is calculated asfollows: ${{{Wt}\quad \% \quad {Bromine}} = \frac{\begin{matrix}{{mL}\quad {of}\quad {sodium}\quad {thiosulfate} \times} \\{{Normality}\quad {of}\quad {sodium}\quad {thiosulfate} \times 8}\end{matrix}}{{Sample}\quad {weight}\quad {in}\quad {grams}}}\quad$

Determination of Hydrogen Bromide:

A weighed aliquot (about 1 mL sample) of the clear reaction mass motherliquor is mixed with 50 mL of deionized water. About 10 drops of 0. 1%aqueous bromocresol green indicator solution is added and titrated with0.5N NaOH solution to a blue end point. Amount of hydrogen bromide iscalculated as follows:${{Wt}\quad \% \quad {HBr}} = \frac{{mL}\quad {of}\quad {NaOH} \times {Normality}\quad {of}\quad {NaOH} \times 8.091}{{Sample}\quad {weight}\quad {in}\quad {grams}}$

Once steady-state reaction conditions are in place, continual monitoringof unreacted bromine content in the liquid phase is unnecessary,. Fromthen on only periodical monitoring is necessary to ensure that theprocess is functioning pursuant to this invention. Moreover, once thesteady-state conditions are in place, the frequency of HBr analyses canbe reduced to periodical checking to be sure that some upset such asline pluggage or etc. has not occurred.

It is possible to estimate the unreacted Br₂ content of the liquid phaseof the reaction mass by the use of colorimetric techniques. A techniquewhich can be used comprises the formation of an acidic (HBr) water andmethanol or ethanol solution. From this solution, several standardsamples are prepared, to each of which is added a different and measuredamount of Br₂. The colors of these sample solutions are then comparedcolorimetrically with the color of the liquid of phase of the reactionmass. A color match is indicative of the amount of Br₂ in the liquidphase. Colorimetric determination for unreacted Br₂ is quite suitable asunreacted Br₂ colors the sample solutions and the reaction mass inaccordance with its concentration. Low concentrations give a pale yellowcolor; intermediate concentrations give a strong yellow color; highconcentrations give an orange color; and the highest concentrations givea dark red color. Unreacted Br₂ concentrations up to about 10,000 ppm,based upon the reaction mass liquid portion, are preferred, althoughsmaller excesses above stoichiometric can be used. As noted above, anexcess of as high as about 35,000 ppm of unreacted bromine in the liquidphase can be tolerated, although typically the excess will not be aboveabout 20,000 ppm, with the a more preferred amount of unreacted brominebeing within the range of from about 50 to about 10,000 ppm.

The unreacted Br₂ concentrations are maintained in the reaction mass solong as bisphenol-A and underbrominated species are likewise present. Ascan be appreciated, the unreacted Br₂ content diminishes as the Br₂reacts, thus, the HBr and hydrogen peroxide feeds, and if used, a Br₂feed, act to replenish the Br₂ in the reaction mass. Using theabove-described colorimetric technique, the unreacted Br₂ content of thereaction mass can be monitored during the process and the unreacted Br₂content within the chosen target range can be maintained, if necessary,by appropriate adjustment of the feed rates to achieve and maintainsteady-state operation. Since there will be tetrabromobisphenol-Aprecipitate in the reaction mass, colorimetric monitoring may requirethat a small stream be taken from the reactor and filtered to remove thesolids before being submitted to a colorimetric technique. It may alsobe possible to read the intensity of the reaction mass color withoutfiltration by the use of reflectance techniques which measure theintensity of the light reflected off of the reaction mass. In all of thecolorimetric cases, the color of the liquid phase of the reaction masscan be used as a way of estimating bromine concentration.

Upon termination of a continuous operation, e.g., for scheduledmaintenance, the excess Br₂ present in the final portion of the reactionmass after completion of the process can be removed by treating thereaction mass with a reducing agent such as sodium sulfite or hydrazine.

Another important consideration in practicing the processes of thisinvention is the reaction mass temperature for the bromination. It isdesirable to use a relatively high temperature so that the brominationof the bisphenol-A to tetrabromobisphenol-A will be sufficiently fast toreduce the extent of tribromobisphenol-A precipitate formation. However,there is a practical limit as to how high the temperature can be. Forexample, temperatures which would cause the production of unacceptablelevels of unwanted by-products or the degradation of thetetrabromobisphenol-A product should not be used.

It is unusual to operate a tetrabromobisphenol-A process at relativelyhigh temperatures, especially when production of a co-product such asmethyl bromide or ethyl bromide is to be minimized. Also, use ofrelatively high temperatures might be expected to complicate the processby increasing the solubility of the tetrabromobisphenol-A in the solventsolution and possibly necessitate a final cooling of, or addition ofwater to, the reaction mass to effect the desired high yieldprecipitation of tetrabromobisphenol-A. The processes of this invention,however, can be operated without excessive coproduction of methylbromide or ethyl bromide, and there is no requirement for a cooling stepto obtain sufficient tetrabromobisphenol-A precipitation.

Operation at relatively high temperatures can contribute to additionalprocess economy and product purity enhancement. Process economy, inpart, can be realized because even at higher reaction mass temperatures,cooling tower water can be used to cool the reactor instead of usingrefrigeration which is required by processes that are operated at lowtemperatures.

Typically temperatures are within the range of from about 30 to about100° C., and preferably are in the range of about 50 to about 100° C.More highly preferred temperatures are within the range of from about 50to about 80° C. Essentially constant and uniform reaction masstemperatures within these ranges are typically maintained when operatinga process of this invention. However, programmed fluctuations intemperature within these ranges may be utilized in continuousoperations, if desired. The most highly preferred temperatures arewithin the range of from about 50 to about 70° C. Temperatures below 30°C. can be used, but the organic solvent to bisphenol-A and/orunderbrominated bisphenol-A weight ratio may well need to be high, sayfrom 8:1 to 15:1. For these ratios, temperatures of 30 to 50° C. may besuitable.

The bromination of bisphenol-A and/or underbrominated bisphenol-A is anexothermic reaction as is the oxidation of HBr with H₂O₂. To control thereaction mass temperature, it may become necessary to remove heat fromthe reaction mass. Heat removal can be effected by running the reactionat reflux with the condenser facilitating the heat removal. If it isdesired to operate at a temperature below the atmospheric boiling pointof the reaction mixture, the reaction can be run under sub-atmosphericpressure.

Generally, the basic concepts of the processes of this invention are notappreciably affected by the process pressure. Thus, the process can berun under sub-atmospheric, atmospheric or super-atmospheric pressure.

The reactor used in the practice of this invention is preferably acontinuously stirred tank reactor. The reaction mass is beingcontinuously formed and a portion thereof is being removed from thereactor during the reaction mass formation. The reactor design should besuch that the average residence time in the reactor is sufficient toensure tetrabromination of substantially all of the bisphenol-A and/orunderbrominated bisphenol-A. Terms such as “continuous feed” and“continuous withdrawal” and terms of analogous import are not meant toexclude interrupted feeds or withdrawals. Generally, such interruptionsare of short duration and may be suitable depending upon the scale anddesign of the reactor. For example, since the tetrabromobisphenol-Aprecipitate will tend to settle near the bottom of the reactor, awithdrawal may be made and then stopped for a period of time to allowfor precipitate build-up to occur prior to the next withdrawal. Such awithdrawal is to be considered continuous in the sense that thewithdrawal does not await the completion of the reactor feeds as ischaracteristic of batch processes. Uninterrupted withdrawal ispreferred, however.

Experimental evidence available to date indicates that the preferredreactor residence time should be within the range of from about 30 toabout 150 minutes when using a stirred-tank reactor and the processconditions which are preferred for that operating mode. Reactorresidence time, as used herein, is the reactor volume divided by theflow rate at which slurry is removed from the reactor.

Workup of the reaction mass being continuously or at least substantiallycontinuously withdrawn from the reactor is not complicated. Since thewater content of the reaction mass is so large and since thetetrabromobisphenol-A is so insoluble in the presence of such an amountof water, there may only be a small benefit in rapidly cooling thewithdrawn reaction mass upon its withdrawal from the reactor. Thebenefit of cooling resides mainly in reducing the vapor pressure ofsolvated gaseous bromides, e.g.,., methyl bromide or ethyl bromide, inthe withdrawn reaction mass prior to the liquid-solids separation. Therealso may possibly be some reduction in rate of continued formation ofthese alkyl bromides. In addition, depending upon the water content ofthe reaction mass, cooling may allow for additional precipitation oftetrabromobisphenol-A from the reaction mass. Additionally, depending onthe separation technique used, cooling the reaction mass may make iteasier to handle downstream from the reactor. Thus, if none of thesefeatures are of concern or relative value, then the reaction mass can besubjected to liquid-solids separation as soon as it can be transportedto the separation equipment. If, however, cooling is desired, thecooling time will depend upon how the reaction mass is to be cooled andto what temperature it is to be cooled. In a laboratory setting, coolingtimes can range from about one minute to about thirty minutes.

Before subjecting the withdrawn reaction mass to liquid-solidsseparation additional water may be added to the reaction mass to ensurethat even more tetrabromobisphenol-A precipitate is formed in thereaction mass. The water addition and precipitation time can be veryshort, e.g, less than about thirty minutes. Use of cool water will alsohave the effect of reducing the temperature of the reaction mass beingtreated.

The liquid-solids separation is readily conducted by use of suchtechniques as decantation, centrifugation, filtration or similarphysical separation procedures. After the recovery of the solids fromthe liquid, the solids are preferably washed with a solution of waterand the particular water-miscible organic solvent used in the reaction.The washing removes essentially all the mother liquor from the solids.The mother liquor typically contains impurities such as tribromophenol,HBr, and hydrolyzable impurities. A typical wash can be a 30 wt %methanol or ethanol in water solution. The washed solids are thenrewashed with deionized water to remove any remaining water-miscibleorganic solvent from the first wash so as to minimize emission problemswhen drying the product.

Individual or combined workup operations on the withdrawn reaction massand on the recovered tetrabromobisphenol-A can be conducted on a batch,semi-continuous, or continuous basis, as desired.

At process initiation for plant startup, it is desirable to charge thereactor with a liquid pre-reaction charge which will become a part ofthe reaction mass upon the commencement of the concurrent feeds. Theliquid charge will provide a stirrable reaction mass and act as a heatsink to moderate temperature changes in the reaction mass. The liquidcharge is preferably comprised of water and the same water-miscibleorganic solvent that is to be fed in the bisphenol-A and/orunderbrominated bisphenol-A solution or slurry. It is preferred that theliquid charge be acidic, e.g., containing from 1 to 20 wt % acid such asHBr, HCl, or the like. The acid seems to promote good color in theinitial tetrabromobisphenol-A produced. Further, during processinitiation it is preferred that the solvent be saturated with solvatedtetrabromobisphenol-A. It is also preferred that the reactor be chargedwith seed particles of tetrabromobisphenol-A during plant startup. Thesaturation of the solvent and the presence of the seed particles bothact to enhance the precipitation of the tetrabromobisphenol-A producedduring the bromination during process initiation. It is most practicalto use a heel from a discontinued prior operation as the liquid charge.The tetrabromobisphenol-A seed particles can be brought over in thereaction mass from a previous discontinued operation, or even from asuitable batch operation. Alternatively, the seed particles can be addedseparately to the heel. If a heel is not available, it is also possibleto use a separate water and water-miscible organic solvent feed, whichare a part of the total solution feed, to form the initial liquidcharge. In this scheme, an initial amount of water and water-miscibleorganic solvent are fed to the reactor prior to the initiation of thesolvated bisphenol-A portion and/or the slurry of underbrominatedbisphenol-A portion of the solution or slurry feed. The only caveat tothis scheme is that there must be apportionment of the various feedsmaking up the solution feed so that there will still be compliance withthe various parameters which define the processes of this invention.

Product of excellent quality can be produced pursuant to this invention.The tetrabromobisphenol-A product can have a purity of 97 wt % andabove, and with a very small tribromobisphenol-A content, if any, ofabout 2 wt % or less. Moreover, it is possible to producetetrabromobisphenol-A product having an APHA color less than about 50(as determined by dissolving 80 grams of tetrabromobisphenol-A productin 100 mL of acetone). Hydrolyzable bromides can also be kept low,generally below about 60 ppm. The process yields are impressive, withyields within the range of from about 95 to about 99% being possible.

As can be appreciated from the foregoing, the water content of thesolvent, the reaction temperature, and the HBr and Br₂ contents in thereaction mass during the bisphenol-A and/or underbrominated bisphenol-Afeed all contribute to obtaining the desired tetrabromobisphenol-Aproduct in an efficient manner. The selection of particular values foreach of these process parameters to obtain the results desired willdepend on the desired output and needs in respect of a particular plantoperation and upon the equipment available. One plant design mayemphasize one benefit of using a process of this invention over otherpossible benefits. Thus, designers of that plant and its process mayselect different process parameter values than those selected by thedesigners of another plant in order to emphasize one or more otherbenefits.

Though preferably designed to minimize the production of methyl bromideor ethyl bromide coproduct, the processes of this invention are readilyadaptable to modification to coproduce methyl bromide or ethyl bromide.

While the foregoing descriptions of the oxidation of HBr generally speakof the HBr being oxidized in the reactor or reaction mass, it is withinthe scope of the processes of this invention to also remove HBr from thereactor and oxidize it outside of the reactor (i.e., in another suitableclosed vessel or like apparatus) and then to send the so-produced Br₂back to the reactor, or to separately generate bromine needed for theprocess by operation of a separate installation wherein HBr from one ormore other sources is oxidized to bromine.

HBr fed to the reactor can be either recycled HBr recovered from theoff-gases of the bromination reaction, or non-indigenous HBr obtainedfrom other sources, or a combination of both such sources.

To achieve the greatest benefits made possible by this invention oneshould, to the extent practicable under the particular set of operatingparameters being used, arrange to reach the steady-state operatingconditions as described herein with as little delay as is feasible. Andonce those conditions have been reached they should be maintained aslong as is practicable during the bromination. An advantage of thepresent continuous mode of operation is that once the steady-state ofoperation within these conditions has been reached, it is possible tomaintain them as long as is desired. In such case reaction mass andprecipitate formed during the startup phases of the operation prior toreaching the selected steady-state conditions can be discarded.

The following Examples are presented to illustrate the practice of, andadvantages made possible by, this invention. These Examples are notintended to limit, and should not be construed as limiting, the scope ofthis invention to the particular operations or conditions describedtherein. The APHA color values set forth in these Examples weredetermined by dissolving 80 grams of the tetrabromobisphenol-A productin 100 mL of acetone.

EXAMPLE 1

A 1-liter flask was equipped with a mechanical stirrer, condenser,thermometer, and a down-drain to continually remove slurry from thereactor. The flask was fitted with three feed tubes (one-eighth inchO.D.) for feeding bisphenol-A solution, 48% HBr solution and 50% H₂O₂solution. The top of the condenser was connected to a vacuum pump. Thetemperature of the reactor was maintained at about 60° C. by controllingthe vacuum at about 26 inches of Hg. Bisphenol-A, HBr and H₂O₂ solutionswere fed to the reactor using peristaltic pumps. The bisphenol-Asolution was prepared by dissolving 800 grams of bisphenol-A in 3200grams of ethanol. A 50 wt % aqueous solution (200 mL) of ethanol wascharged to the reactor as the heel. The above bisphenol-A solution, and50 wt % aqueous H₂O₂ and 48 wt % aqueous HBr solutions were fed to thereactor at flow rates of about 13.0 mL/min., 1.9 mL/min. and 8.0mL/min., respectively. HBr and H₂O₂ feeds were kept stoichiometricallyahead of the bisphenol-A feed and as a result, the reaction mass waspale yellow. The temperature of the reactor rose to about 60° C. and waskept at that temperature by reflux cooling. The product slurry wascontinually drained from the bottom of the reactor to keep a constantlevel in the reactor. The slurry was filtered and washed first with 30wt % aqueous ethanol and then with deionized water. The washedprecipitate was dried and analyzed. The product tetrabromobisphenol-Ahad APHA color of 30 and a purity of 99.4%. The mother liquor contained14.1% HBr and 0.8% Br₂.

EXAMPLE 2

The reactor flask was fitted with a dip tube for feeding bromine vaporand three feed tubes which terminated in the vapor phase, for feedingbisphenol-A solution, 48 wt % HBr solution and 50 wt % H₂O₂ solution.The bromine tube from the pump was connected to a nitrogen inlet and abromine vaporizer and a gas outlet were connected to the diptube in thereactor. A 50 wt % aqueous solution (200 mL) of ethanol was charged tothe reactor as the heel. A 20 wt % solution of bisphenol-A in ethanol,the 50 wt % aqueous H₂O₂ solution, the 48 wt % aqueous HBr solution, andBr₂ were fed concurrently to the reactor at flow rates of about 9.0mL/min., 1.5 mL/min., 7.5 mL/min. and 0.7 mL/min., respectively. Thetemperature of the pale yellow slurry rose to about 60° C. and was keptat that temperature by reflux cooling. The product slurry wascontinually drained to keep a constant level in the reactor. The slurrywas filtered and washed first with 30 wt % aqueous ethanol and then withdeionized water. The precipitate was dried and analyzed. The producttetrabromobisphenol-A had a purity of 99.8% and an APHA color of 25.

It is to be understood that the processes of this invention can be runin combination with processes having process parameters not of thisinvention. For example, if it is desired to produce an intermediateamount of methyl bromide ethyl bromide, a process similar to a processdescribed above using methanol or ethanol as the water-miscible organicsolvent but with process parameters which promote the formation ofmethyl bromide or ethyl bromide, such as, for example, use of a lowwater content in the vicinity of about 10 wt %. This process could berun for a period of time and then could be interrupted with theimposition of the parameters of this invention so as to diminish methylbromide or ethyl bromide production. In this way, the methyl bromide orethyl bromide production can be controlled within desired productionlimits by combining both processes.

This invention is susceptible to considerable variation in its practice.Therefore the foregoing description is not intended to limit, and shouldnot be construed as limiting, the invention to the particularexemplifications presented hereinabove. Rather, what is intended to becovered is as set forth in the ensuing claims and the equivalentsthereof permitted as a matter of law.

That which is claimed is:
 1. A process for producingtetrabromobisphenol-A, which process comprises providing a liquid phasereaction system in which there is directly formed atetrabromobisphenol-A precipitate by the bromination of bisphenol-Aand/or underbrominated bisphenol-A using an excess of bromine over thestoichiometric amount theoretically required to producetetrabromobisphenol-A, more than 50 mole percent of the bromine in thereaction system being generated in situ by oxidizing HBr, at least partof which HBr is continuously fed to said reaction system as HBr.
 2. Aprocess of claim 1 wherein the HBr that is continuously fed to saidreaction system is fed as aqueous hydrobromic acid.
 3. A process ofclaim 1 wherein HBr co-product is also oxidized in situ to bromine.
 4. Aprocess of claim 1 wherein the bromination is conducted in the presenceof an amount of HBr that is high enough to protect thetetrabromobisphenol-A being produced from excessive color development.5. A process of claim 1 wherein the bromination is conducted at suchrate that (i) there is insufficient opportunity for significantprecipitation of the intermediate, tribromobisphenol-A, to occur, and(ii) while the bisphenol-A and/or underbrominated bisphenol-A is/arebeing brought into contact with unreacted bromine in the liquid phase ofthe reaction mass, tetrabromobisphenol-A is being produced substantiallycontinuously.
 6. A process of claim 5 wherein the yield of thetetrabromobisphenol-A as it is being produced substantially continuouslyis at least about 90% based on the amount of the bisphenol-A and/orunderbrominated bisphenol-A already fed.
 7. A process of claim 6 whereinsaid yield is at least about 95%.
 8. A process of claim 1 wherein thetetrabromobisphenol-A produced has an APHA color of less than about 100,the APHA color being determinable by dissolving 80 grams of thetetrabromobisphenol-A product in 100 mL of acetone.
 9. A process ofclaim 1 wherein the HBr that is continuously fed to said reaction systemis fed as aqueous hydrobromic acid; wherein HBr co-product is alsooxidized in situ to bromine; wherein the bromination is conducted in thepresence of an amount of HBr that is high enough to protect thetetrabromobisphenol-A being produced from excessive color development;wherein the bromination is conducted at such rate that (i) there isinsufficient opportunity for significant precipitation of theintermediate, tribromobisphenol-A, to occur, and (ii) while thebisphenol-A and/or underbrominated bisphenol-A is/are being brought intocontact with unreacted bromine in the liquid phase of the reaction mass,tetrabromobisphenol-A is being produced substantially continuously; andwherein the yield of the tetrabromobisphenol-A as it is being producedsubstantially continuously is at least about 90% based on the amount ofthe bisphenol-A and/or underbrominated bisphenol-A fed.
 10. A process ofclaim 9 wherein the tetrabromobisphenol-A produced has an APHA color ofless than about 100, the APHA color being determinable by dissolving 80grams of the tetrabromobisphenol-A product in 100 mL of acetone.
 11. Aprocess of claim 9 wherein said yield is at least about 95%.
 12. Aprocess of claim 10 wherein said yield is at least about 95%.
 13. Aprocess of claim 8 wherein said APHA color is 50 or less.
 14. A processof claim 10 wherein said APHA color is 50 or less.